Ongoing development activities aimed at increasing computer processor speed and data transmission rates, together with the increasing number of applications requiring display, tabulation, synthesis, or transformation of enormous amounts of data, are creating an accelerating demand for high capacity data storage systems. Examples include multimedia databases with full color images and audio, CAD/CAM drawings and associated data, full text databases with access to daily newspapers and other periodical information, and scientific data involving empirical measurements or results from mathematical calculations. Any of these applications can involve multiple terabytes of data, requiring high capacity data storage systems which use large amounts of floor space, power and cooling.
Traditionally, high capacity data storage involves large diameter, expensive disk files grouped together in sets of 2, 4, or 8 and accessed through an equally large and expensive control unit. In recent years, the commoditization of small diameter (51/4 inches or less) disk files has led to a revolution in high capacity data storage through which the small groups of large diameter disk files have been replaced by larger groups (typically 8 to 64 disk files) of small diameter, inexpensive disk files. This metamorphosis has gained additional impetus through the development of new techniques for grouping small disks that dramatically increase overall system reliability while sharply decreasing data access times, floor space requirements, and power consumption. These techniques have become popularly known as RAID technology (redundant arrays of inexpensive disks), which categorizes the trade-off between reliability and redundancy using RAID levels. Thus, RAID-1 is used to indicate mirrored storage, the most reliable but also the most costly alternative. RAID-5 is used to indicate parity protected storage in which parity is spread across a set of disk files. Other RAID levels are available, and are discussed in detail in the literature. Similarly, other data protection mechanisms are available which are useful in grouping numerous small disk files.
Existing data storage systems built around RAID technology typically include approximately 10 to 100 individual disks housed in one or more racks, spaced from one another to allow cooling air to flow between them. This approach has proven sufficient to date because the total power and thermal loading created by 10 to 100 disks is readily manageable, and because the total space occupied by such a system, even including ample space between the disk files, is manageable.
However, existing packaging and power handling concepts are not sufficient for use with denser and larger arrays required to store high volume data. For example, at a typical power consumption rate of 50 mW/megabyte (M-byte), a 10 terabyte disk array would required 500K W of input power to service the disk files alone. This would create a power requirement unacceptable to most users, and a cooling problem of sizeable proportions. Moreover, using today's technology tens of thousands of small disk files are required to provide this level of storage capacity. This would translate into a significant floor space requirement which also is unacceptable to many users. And, any attempt to reduce the spacing between individual disk files as a means of reducing the overall floor space requirement would worsen the cooling problem, rending the data storage system inoperative. Thus, what is needed to meet all user criteria is a data storage system having a large number (potentially tens of thousands) of closely spaced small disk files with low power and thermal requirements.